World Wind by NASA

NASA has open source software called World Wind, the newest version of which is now available. Not only can you glimpse every corner of the globe from incredibly close or incredibly far away - but it's easily navigable and you can execute screen captures and download them to your computer as JPEGs. It's a lot of fun, and best of all - it's free.

http://worldwind.arc.nasa.gov/

"World Wind lets you zoom from satellite altitude into any place on Earth. Leveraging Landsat satellite imagery and Shuttle Radar Topography Mission data, World Wind lets you experience Earth terrain in visually rich 3D, just as if you were really there.

Virtually visit any place in the world. Look across the Andes, into the Grand Canyon, over the Alps, or along the African Sahara."